It's not floating and it's no different with the probe connected,
however difficult this may be to believe for us.
Perhaps the AM503A schematic is wrong and there isn't 3V there, has
anyone actually checked on a AM503A?
On Thu, Nov 5, 2015 at 7:49 PM, firstname.lastname@example.org [TekScopes]
Could the supply voltages at connector A and D be floating w.r.t. ground? Did you also measure between A and D?